Electronic data is commonly stored on discs of various types. Disc drives hold and rotate the disc while positioning a read/write head over the disc to read data from it or write data to it. The head typically comprises a read/write transducer formed on the trailing surface of a slider. When the disc media is rotated, a thin film of air forms between the disc and an air bearing surface (ABS) of the slider. During operation of the disc drive, the head is said to “fly” over the surface of the rotating media, with the ABS being disposed just above the disc surface. The thin film of air formed between the ABS and the disc surface is known as the air bearing. The very small separation distance between the transducer of the flying head and the surface of the disk is referred to as the “flying height.” When the flying head is suspended above the recording disc in this manner, it can be moved over a desired concentric track of the disc to access data stored on that track.
The flying height of the head is a critical factor affecting the density of the magnetic data that can be stored on the disc. In recent years, the magnetic recording industry has strived to increase the data storage density in both longitudinal and perpendicular recording technologies by employing various techniques aimed at decreasing the average flying height of the head over the rotating magnetic media.
A perpendicular magnetic recording head differs from the more traditional longitudinal recording head in the direction of the magnetic flux orientation with respect to the magnetic disk medium. During a write operation, a perpendicular recording head directs the magnetic flux in a direction substantially normal to the surface of the magnetic disk. In contrast, the magnetic flux generated by a longitudinal recording head is generally in the plane of the surface of the magnetic disk. A perpendicular magnetic recording head with enhanced magnetic field strength is disclosed in U.S. Pat. No. 6,791,793, which is herein incorporated by reference. Perpendicular magnetic recording heads and methods of operation are also taught in U.S. Pat. Nos. 6,847,509; 6,834,026; 6,822,829; 6,816,339; and 6,813,115.
In one prior art technique for reducing the flying height of the magnetic head is to incorporate a heating element into the slider to temporarily heat a portion of the head to cause the transducer elements to move closer to the rotating disc, thereby reducing the flying height during periods of reading and writing. This allows the flying height to be low during reading and writing, and to be high at other times to enhance the durability of the head-disk interface. The technique of reducing flying height when reading and writing is commonly known as “dynamic flying height” (DFH) actuation. By way of example, U.S. Pat. No. 6,775,103 teaches a slider head having a patterned heating element which selectively heats the edge of the leading slider surface to cause the head to fly closer to the rotating disc. Similarly, U.S. Pat. No. 5,991,113 discloses a resistive heating element embedded within the slider body just ahead of the transducer. Application of power to the heating element causes the pole tips of the transducer to protrude toward the data recording surface relative to the air bearing surface of the slider, such that the flying height at the location of the transducer is reduced.
Magnetic recording heads that include a heater disposed in an overcoat layer for thermally expanding the surrounding layers, thereby adjusting the distance between the transducer device and the hard disc, are disclosed in U.S. Patent Application Publications US 2004/0184192 and US 2004/0130820. U.S. Patent Application Publication US 2004/0075940 teaches a heating element that is either physically located in the overcoat layer between the write transducer and a passivation layer, or between the read transducer and the slider body. Additionally, U.S. Patent Application Publication US 2003/0099054 discloses a thin-film magnetic head having a heater formed at a position opposite to the air-bearing surface with respect to the magnetic head elements.
Resistive heating elements have also been used in so-called “thermally assisted” magnetic recording (TAMR), wherein the magnetic material in the media is locally heated to near or above its Curie temperature in order to lower the coercivity of the recording media during writing. At ambient temperature, the coercivity is high enough for thermal stability of the recorded bits. A good example of a TAMR disk drive is found in U.S. Pat. No. 6,493,183, which discloses a thin-film write head having a resistive heater located in the write gap between the pole tips of the write head.
A variety of problems have plagued prior art head designs that utilize Joule heating elements for dynamically controlling the flying height of the read/write transducer. One problem has been excessive thermal stress caused by localized heating of the slider and transducer materials. Relatively high power to the heater is often required to produce sufficient pole tip protrusion. Other problems associated with thermal heating of slider heads include the difficulty in achieving an optimal transducer protrusion profile, overheating of the magnetoresistive reading element, deformation of the shape of the slider, and poor control over pole tip protrusion. For instance, designs that include a heater element disposed in the overcoat layer often suffer from disproportionate expansion of the overcoat material such that the overcoat material contacts the surface of the magnetic disc, thereby increasing the distance between the magnetic recording elements and the disc surface. Many of these problems may lead to deleterious consequences in prior art magnetic recording heads.
Another past approach involves controlling the flying height dynamically by applying a voltage between the flying head and the magnetic storage medium. The applied voltage controls the vertical movement of the head to increase or decrease the flying height by electrostatic forces. This technique is described in U.S. Pat. No. 6,529,342. One major drawback of the electrostatic force approach, however, is the inability to maintain precise control over the flying height. Another approach involves piezoelectric head-positioning techniques. Such techniques are disclosed in U.S. Pat. Nos. 6,577,466 and 5,943,189. A magnetic disk drive that incorporates a piezoelectric element with a resistive heater located between the read transducer and the slider body is described in U.S. Patent Application Publication US 2004/0165305. A drawback of such piezoelectric techniques, however, is that they are typically difficult to manufacture without thermally damaging the read transducer.
In yet another approach, U.S. Pat. No. 6,707,646 discloses a method and apparatus for dynamically controlling the flying behavior and height of a read/write head by manipulating the spring constant of the suspension. The spring constant is changed by locally varying the material temperature of the suspension arm using a small heater deposited on the surface of the suspension arm. This technique suffers from serious reliability and control problems.
Thus, there is an unsatisfied need for a solution to the problem of achieving a low flying height during reading/writing processes while avoiding or reducing the problems inherent in prior art DFH actuation approaches.